Animal hypnosis: an attempt to reach a definition.

Animal hypnosis is a prolonged immobility response which may be defined according to several physiological parameters. In the rabbit, EEG, hyppocampal rhythmic activity, spinal reflexes and local cerebral glucose utilization are modified during this condition. The duration of the response is affected by persistent nociceptive stimuli. Corticosterone plasma levels are correlated with individual susceptibility and elevated when habituation to hypnosis occurs. Testosterone metabolism in the hypothalamus is found decreased after a single trial and increased following repeated trials. The possible importance of these modifications is discussed.